Wireless access communications technologies, such as Bluetooth, wireless local area networks (WLAN), ultra wideband (UWB), and sensor radios (e.g. ZigBee) are becoming increasingly available and important for portable devices. Such technologies often complement more traditional cellular access technologies to provide a portable device with expanded communications capabilities.
Each individual access technology is often well-suited for particular types of uses and applications. Thus, for a device to provide its user with the ability to experience a multitude of applications (e.g. wireless headset, fast internet access, synchronization, and content downloading), it is desirable for a device to support multiple access technologies.
WLANs are local area networks that employ high-frequency radio waves rather than wires to exchange information between devices. IEEE 802.11 refers to a family of WLAN standards developed by the IEEE. In general, WLANs in the IEEE 802.11 family provide for 1 or 2 Mbps transmission in the 2.4 GHz band (except IEEE 802.11a) using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS) transmission techniques. Within the IEEE 802.11 family are the IEEE 802.11b, IEEE 802.11g, and IEEE 802.11a standards.
IEEE 802.11b (also referred to as 802.11 High Rate or Wi-Fi) is an extension to IEEE 802.11 and provides data rates of up to 11 Mbps in the 2.4 GHz band. This allows for wireless functionality that is comparable to Ethernet. IEEE 802.11b employs only DSSS transmission techniques. IEEE 802.11g provides for data rates of up to 54 Mbps in the 2.4 GHz band. For transmitting data at rates above 20 Mbps (or when all devices are IEEE 802.11g capable), IEEE 802.11g employs Orthogonal Frequency Division Multiplexing (OFDM) transmission techniques. However, for transmitting information at rates below 20 Mbps, IEEE 802.11g employs DSSS transmission techniques. The DSSS transmission techniques of IEEE 802.11b and IEEE 802.11g involve signals that are contained within a 20 MHz wide channel. These 20 MHz channels are within the Industrial Scientific Medical (ISM) band. IEEE 802.11a employs OFDM transmission techniques and provides for data rates of up to 54 Mbps in a 5 GHz band.
Wireless personal area networks (WPANs) are used for exchanging information with devices, such as portable telephones and personal digital assistants (PDAs), that are within the proximity of an individual. Examples of WPAN technologies include Infrared Data Association (IrDA) and Bluetooth.
Bluetooth defines a short-range radio network (also referred to as a piconet). It can be used to create ad hoc networks of up to eight devices, where one device is referred to as a master device and the other devices are referred to as slave devices. The slave devices can communicate with the master device and with each other via the master device. Bluetooth devices are designed to find other Bluetooth devices within their communications range and to discover what services they offer. A typical range for a Bluetooth piconet is 10 meters. However, in certain circumstances, ranges on the order of 100 meters may be attained.
ZigBee is a wireless communications access technology that, like Bluetooth and IEEE 802.11b, operates in the 2.4 GHz (ISM) radio band. Zigbee can connect up to 255 devices per network and provide for data transmission rates of up to 250 Kbps at a range of up to 30 meters. While slower than IEEE 802.11b and Bluetooth, ZigBee devices consume significantly less power.
High rate WPAN schemes are currently under development that employ wireless technologies, such as ultra wideband (UWB) transmission, which provides for the exchange of information at higher data rates. Since gaining approval by the Federal Communications Commission (FCC) in 2002, UWB techniques have become an attractive solution for short-range wireless communications. Current FCC regulations permit UWB transmissions for communications purposes in the frequency band between 3.1 and 10.6 GHz. However, for such transmissions, the average spectral density has to be under −41.3 dBm/MHz and the utilized −10 dBc bandwidth has to be higher than 500 MHz.
There are many UWB transmission techniques that can fulfill these requirements. A common and practical UWB technique is called impulse radio (IR). In IR, data is transmitted by employing short baseband pulses that are separated in time by gaps. Thus, IR does not use a carrier signal. These gaps make IR much more immune to multipath propagation problems than conventional continuous wave radios. RF gating is a particular type of IR in which the impulse is a gated RF pulse. This gated pulse is a sine wave masked in the time domain with a certain pulse shape.
As discussed above, it is desirable for a device to support multiple access technologies. One approach to this is furnishing the device with multiple radios-one for each access technology. However, this approach brings several drawbacks. For instance, every additional radio brings forth an added cost as well as the need for additional physical space on a circuit board (and potentially a dedicated antenna). Moreover, controlling several radios adds complexity to device control. In addition, each separate radio creates a distinct reliability issue. With regard to the development of new devices, the needed effort to design and provide new radios for certain types of links causes delays and additional project risks.
Accordingly, there is a need to support multiple access technologies without furnishing devices with additional radios.